This section introduces aspects that may be helpful in facilitating a better understanding of the invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
Demands for higher data rates for mobile services are steadily increasing. At the same time modern mobile communication systems as 3rd Generation systems (3G) and 4th Generation systems (4G) provide enhanced technologies, which enable higher spectral efficiencies and allow for higher data rates and cell capacities. The demands are growing for both directions of transmission, in the DownLink (DL) for transmission from the network infrastructure to a mobile transceiver, as well as in the UpLink (UL) for transmission from a mobile transceiver to the network infrastructure.
Current mobile communication systems increasingly rely on small cell base stations. Small cell base stations can be used to cover areas where the macro cell base stations do not provide sufficient coverage and capacity and to improve network efficiency. Small cells may appear to be an efficient approach to increase the capacity and improve network efficiency. It is recognized, however, that the potential attractiveness of small cells might only be realized if installation costs can be controlled. Two requirements for a small cell installation might be electrical power and backhaul, which when provided by wired connections may often be costly. A wired connection for electrical power may be eliminated by deriving power from a small wind turbine or solar panel and charging storage batteries, and by decreasing internal power consumption. The second small cell wired connection may be eliminated by using wireless backhaul.
To decrease internal power consumption a repeater-type small cell might be used, that on downlink receives a complex-valued analog baseband signal on a carrier frequency from a backhaul link and re-transmits the baseband signal at an access carrier frequency that accommodates one or more small cell users, and on the uplink receives from one or more small cell users their combined transmitted signals on an access link and re-transmits their combined baseband signals on the backhaul uplink. The repeater small cell might mainly comprise pre-amplifiers, frequency converters, filters and power amplifiers so it might be designed for low-power consumption.
US patent application 2012/238202 A1 discloses a method for transmitting data using relay stations. The method is based on a base station sending a reference signal to relay stations of a mobile communication system via a backhaul link. The relay stations calculate channel parameters based on the received reference signal, and transmit said parameters back to the base station. The base station uses the channel parameters to determine scheduling information for the backhaul link, and transmits the scheduling information to the relay stations. US patent application 2008/227461 A1 discloses a mobile communication system comprising a base station and relay stations. Based on (data or pilot) transmissions by relay stations, the base station calculates adjustments of a transmission power to be used by the relay stations for a link to the base station or for links to other relay stations (for multi-hop relaying).